The present invention is directed to a device for electrical function testing of wiring matrices, particularly of printed circuit boards.
In automatic testing units and adaptors for printed circuit boards equipped with or without components as well as for wiring matrices in solder or crimp technology, the contacting of selected measuring locations is usually undertaken via resilient test probes. The resilient test probes are arranged according to the grid dimension of the wiring matrix to be tested and are secured with spring sleeves that are pressed into a carrier plate and into which the test probes are inserted. The smallest distance between the measuring locations as well as the current load via the diameter of the resilient test probes are usually decisive in the selection of the test probes. However, 0.69 .mm is cited as a lower limit dimension for the diameter of the probe (Elektronik Produktion und Prueftechnik, November 1979, pages 472 and 473).
Conductivity and insulation measurements between test locations formed by the grid points according to the printed circuit board layout are performed with known devices for electrical function testing of printed circuit boards. Since the resilient test probes provided for contacting the test locations must be arranged in a grid pattern corresponding to the printed circuit board, the construction of such devices is increasingly more difficult because of the decreasing grid dimension and the increasing areas of the printed circuit boards. Thus, an arrangement of the resilient test probes in grid dimensions below 1.0 mm cannot reliably provide precision, mechanical contacting of the test locations. The plurality of required leads and switch elements also increases with the number of measuring locations that, for example, can amount to as many as a hundred thousand. Such an apparatus is very complex resulting in high costs. Further, the probability of a complete contacting of the printed circuit board decreases considerably with the plurality of measuring locations.
EP-A-0 102 565 discloses a device for the electrical function testing of wiring matrices wherein the ohmic contacting of the measuring locations is replaced by non-touching, ionic contacting via gas discharge paths. To this end, a plurality of gas discharge channels provided with electrodes are located in a carrier plate that can be placed onto the wiring matrices. Gas discharge channels in a frame of the wiring matrices are open in the direction toward the measuring locations. When two selected measuring locations are connected to one another in an electrically conductive fashion by an interconnect, then the associated gas discharge channels form two series-connected gas discharge paths that can be ignited by applying an adequately high voltage to the electrodes. A current flow that can be evaluated for testing purposes results with the ignition of the gas discharges. When the ignition of the gas discharges fails to occur or when too low a current flows after an ignition, it can be concluded that an interrupted connection exists or that an electrically conductive connection was not formed when the wiring matrix was constructed. When an alternating voltage is superimposed on the voltage applied to the electrodes, then the resulting current change can be measured in a phase-sensitive manner relative to the applied alternating voltage and can be utilized for identifying the resistance of a connection existing between the selected measuring locations. The known device thus provides conductivity and insulation measurements, whereby an extremely high reliability is achieved by avoiding ohmic contacts. In particular, wiring matrices having small grid dimensions of the measuring locations down to 0.1 mm can be reliably tested with the principle of ionic contacting of the measuring locations via gas discharge channels which can be constructed in extremely small dimensions. However, for a high plurality of measuring locations in a wiring matrix, problems continue to occur that can be attributed to the numerous leads and switch elements for the connection of the electrodes of the gas discharge channels.